1. Field of the Invention
The invention relates generally to surgical saws. In particular, the invention relates to a system including a unique drive mechanism and a uniquely shaped surgical saw blade adapted to cut a generally cylindrical bone plug. More particularly, the invention relates to a surgical saw and method for harvesting a bone-tendon-bone ligament graft.
2. Description of the Prior Art
In certain surgical procedures bone blocks are cut from the bone at the end of a tendon to produce an artificial ligament in the form of a bone-tendon-bone graft. For example, for use in cruciate ligament reconstruction, bone-tendon-bone ligament grafts are often created by cutting a bone block from the patella and tibia and including a portion of the tendon extending between these two bones. Such a graft is then inserted into and secured within prepared bone tunnels in the tibia and femur in order to simulate the function of anterior or posterior cruciate ligaments. The bone plugs are generally secured within the bone tunnel by an interference screw which is threaded into the space between the bone plug and the tunnel wall. Since the bone tunnels are generally prepared by reamers, drills or core drills, the cross-section of the bone tunnels is circular. However, known methods of harvesting bone-tendon-bone ligament grafts produce bone plugs having generally rectilinear shapes which are then shaped to better fit in the tunnels. The production of a bone-tendon-bone graft generally involves cutting two parallel incisions on each side of the middle third of the patellar tendon and then making a three-sided, rectangular cut in the bone at each end of the tendon. An osteotome is then used to remove the bone blocks. Each bone block must then be trimmed to fit within the cylindrical bone tunnel which is typically on the order of 8-10 mm in diameter. While most known methods for producing bone-tendon-bone ligament grafts result in the preparation of bone plugs having a generally trapezoidal or other rectilinear cross-section, it is often preferred to have bone plugs having a cylindrical cross-section in order to produce a better fit between the bone plug and the pre-drilled bone tunnel into which the bone plug must fit. It is desirable to have the bone plugs conform to the shape of the bone tunnel as much as possible in order to promote healing and bony ingrowth of the plug into the tunnel wall.
The preparation of cylindrical bone plugs is known since various surgical procedures often require the preparation of cylindrical or substantially cylindrical bone plugs. Such bone plugs are generally created with the use of devices or instruments commonly referred to as trephines, circular bone saws, core drills, etc. In most of these applications, the circular cross-section of the cylindrical bone plug lies perpendicular to the axis of the circular device. Such devices are either unsuitable or difficult to use in the production of bone-tendon-bone ligament grafts.
One known device for harvesting the bone of a bone-tendon-bone graft is disclosed in U.S. Pat. No. 5,320,115 (Kenna). This device incorporates a powered saw having a cylindrical core drill which is oscillated about its axis and introduced into the bone at each end of the tendon in a direction toward the tendon. After the bone is cut, the core drill must be removed and used to cut the other bone, again toward the tendon. The core drill must be tilted as it is advanced in order to produce the relatively cylindrical bone plug and avoid cutting the tendon.
Another saw adapted to produce cylindrical bone plugs is disclosed in U.S. Pat. No. 5,092,875 (McLees). This patent discloses a circular blade having a peripheral drive arm extending radially outwardly from the body of the blade. The drive arm is oscillated along a semi-circular arc so that the circular blade oscillates about its axis and is able to cut a continuous length of cylindrical bone plug. While this device is capable of producing a bone-tendon-bone graft with cylindrical bone plugs, in actual practice this device is difficult to use. Moreover, the method shown in this patent does not facilitate the production of a partially cylindrical graft which may be desirable in certain situations.
Because bone plugs are often secured by interference screws inserted into the space between the plug and the tunnel wall, totally cylindrical bone plugs may not be desirable. Other applications may find totally cylindrical bone plugs desirable, but for many bone-tendon-bone ACL reconstructions the bone plugs should be produced with a flat so a space remains between the plug and the tunnel wall into which an interference screw will fit. No known prior art devices can easily produce such a plug shape in a bone-tendon-bone graft.
It is accordingly an object of this invention to produce a bone saw system for harvesting a bone-tendon-bone graft.
It is also an object of this invention to produce a flat, ring blade capable of cutting tissue by oscillating about its axis.
It is a further object of this invention to produce a ring blade capable of beginning the cut into a bone at either end of a tendon from the tendon side of the bone.
It is also an object of this invention to produce a bone saw system in which the blade may be attached to the drive unit after the blade has been properly positioned adjacent tissue to be cut.
It is an additional object of this invention to produce a ring blade capable of being easily attached and detached from a drive unit.
It is an object of this invention to produce a bone saw which can produce a substantially cylindrical bone plug of any desired length.
It is an object of this invention to produce a bone saw which can produce a substantially cylindrical bone plug having a flat surface along one side thereof, the size of this flat surface being controllable.
It is also an object of this invention to produce a ring blade capable of being attached to a drive unit in a selected direction so that the cut may be produced by either a pulling motion or a pushing motion.
It is also an object of this invention to produce a ring blade adapted to enable the formation of a longitudinally curved surface along a selected point of the bone plug.
It is an additional object of this invention to provide a method of harvesting a bone-tendon-bone plug through the use of a ring blade.
It is also an object of this invention to produce a bone saw system and method for harvesting a bone-tendon-bone graft such that the bone portions of the graft are aligned with the width of the tendon at each end of the graft.